1. Field of the Invention
The present invention relates to a seal mechanism for a butterfly valve with press contacting seal means functional against the reaction forces in both inflow and outflow directions, in which the sealing by a press contact between the valve body and the valve seat on the valve casing will be realized at the highest effectiveness upon closure of the valve.
2. Description of the Prior Art
The conventional butterfly valves of this kind have a construction in which the sealing by press contact between the outer periphery of the valve body and the receiving face of the seat metal disposed on the inner wall of the valve casing is effective preferentially in the direction of positive dynamic pressure.
In such a valve structure as above, however, not only the seal effect in the direction of positive dynamic pressure is insufficient but the sealing in the direction of negative dynamic pressure is scarcely reliable. Thus, conventional butterfly valves are apt to suffer from leakage troubles, requiring thus considerable maintenance costs, repair works and times with an additional disadvantage of necessity for concurrent employment of non-return valves and other valve means in the case where a flow loop is formed in the pipe line arranement, resulting in an additional investment cost.